Well Managed Cooling Towers Can Save Water, Energy and Money

By Warren Tenney

There is a good chance that a cooling tower system helps to cool the buildings where you work, shop and play. There are about 12,000 cooling towers operating in Phoenix Metropolitan area schools and office buildings, hospitals, industrial facilities, movie theaters, libraries and grocery stores. By design, these systems demand a high volume of water to operate. How these systems are routinely maintained makes a big difference in just how much water and energy a building uses – or saves - each year. That’s why conservation experts from some AMWUA cities are trained to help businesses understand how their cooling towers work and offer ways to save energy, water - and money.

How it works: Cooling towers are different than home air conditioning systems, which use vaporized refrigerant. A cooling tower works by harnessing the cooling effect of water evaporation. Much like swamp coolers, cooling towers operate on the basic understanding that when hot and dry air passes over water (or through it) the water absorbs the heat and the air gets cooler.

Cooling towers are loud, industrial, hardworking machines that are typically hidden on rooftops or behind walls. These systems consist of a large industrial looking metal box, a water treatment system that looks like a collection of small tanks and valves, and a network of water pipes, moving water throughout the system. Buildings usually have two cooling towers, in case one should fail. On very hot summer days, both units may be needed to keep spaces cool. Operating in conjunction with the cooling tower is a system that circulates chilled water through a building cooling it down and sending the water back to the cooling tower to re-chill. The primary function of the cooling tower is to facilitate as much evaporation as possible to efficiently cool the circulating water.

The problem with hard water: Cooling towers in Arizona become less efficient as scale builds on the equipment due to our “hard” water, which is caused by natural minerals found in our desert water supplies. The concentration of mineral buildup can force a cooling tower’s fan to run more often and scaling can ruin a tower altogether requiring it to be replaced more often.

The secret to efficiency: Chemicals used to treat cooling tower water can prevent scale from forming by keeping minerals from hardening on the metal surfaces. The wrong treatment can cause more water to be used and diminish water efficiency. A good cooling tower professional knows the right chemical balance to prevent scale build up and maximize the water reuse inside a tower.

Improving desert cooling towers: Here’s what you need to know when talking to the professional who operates your building’s cooling tower.

Once the system reaches a certain concentration of minerals, a portion of the system water must be dumped and fresh water, or “make up” water, added to the system.

The rate at which water is dumped and more water added is called Cycles of Concentration. (Cycles of Concentration measure the degree to which the solids or minerals are becoming concentrated within the circulating water.)

In our desert cities, a metric for a well-run, efficient cooling tower would be in the range of 2.5 to 3 Cycles of Concentration. In cities with softer water, such as in California, an efficient cooling tower can run 3 to 20 Cycles of Concentration, depending on the source of the water, the treatment of the water and maintenance practices.

In desert cities, increasing the Cycles of Concentration from 1 or 2 up to 3 cycles saves the most water. For example, a 109-ton cooling tower running 1,610 hours per year and operating with 2 Cycles of Concentration uses 637,560 gallons of water per year. That same cooling tower operating at 3 Cycles of Concentration will use about 478,170 gallons per year. That saves nearly 160,000 gallons per year.

The Town of Gilbert’s conservation professionals recently evaluated the efficiency of cooling towers on several town-owned buildings and were pleased to discover that the city’s contracted professional was operating its cooling towers at 2.5 to 2.7 Cycles of Concentration. The team had a few recommendations to help each cooling tower reach 3 Cycles of Concentration. The most important one is adding technology that senses when incoming water quality changes and automatically adjusts the chemicals in the water inside the tower. Instead of running more fresh water through the tower to keep scale down, this technology can adjust the treatment chemicals to help re-use water inside the tower longer.

There are cooling towers throughout the Valley that use water only once before flushing. That means the vendor isn’t utilizing the chemical treatment system properly or something within the system needs to be fixed. In addition to chemical and water management, poor maintenance of float valves and other cooling tower components can result in continuous water waste. Here’s the question for owners and managers of commercial buildings: Is it time to ask your vendor about your cooling towers and call in your city’s professional to help? With thousands of cooling towers in the Valley, getting the most out of cooling systems saves money for businesses and institutions and saves water for all of us.

For 49 years, Arizona Municipal Water Users Association has worked to protect our member cities’ ability to provide assured, safe and sustainable water supplies to their communities. For more water information visit www.amwua.org.